1. Field of the Invention
This invention relates to engine tuning systems where parameters controlling the engine efficiency of operation are modulated so that signals are derived that represent corresponding deviations from an optimum point of operation and said signals are used to control said parameters so that the engine is maintained at a desired optimum point of operation.
2. Description of the Prior Art
Systems that control and tune engines, and in particular internal combustion engines, have been operated and described in the literature. In the Society of Automotive Engineers (SAE) publication No. SP-393 (IEEE Catalog Number 75H0976-1VT), for example, dated February 1975 several engine control systems are described that are designed to improve the performance and fuel economy of internal combustion engines.
Certain control components are always included in the above systems that serve the function of modulating at least one of several parameters that affect engine performance. Modulation, or in other words variation of said parameters, is required at least for the compensation of environmental changes that cause shifts from the optimum operating point of the engine. In optimizing control systems such as described on pages 155 to 182 of said SAE publication No. SP-393 the modulation or dithering of said parameters is also required for the sensing of shifts in the operating point of the engine. A study of control systems in general and the above mentioned references in particular confirms the fact that the effectiveness of control and speed of response to control commands depends directly on the speed with which said control parameters can be changed or modulated. This speed presents a basic limitation on the effectiveness of said control systems and is caused essentially by inertia or stored energies involved whenever force has to be exerted inorder to cause movement of any actuator modulating a control parameter. In fuel injected engines, for example, a considerable force is needed to cause liquid fuel to flow through small orifices into the engine intake duct and within very short periods of time. This requires a considerable amount of energy which results in injectors with a certain size or bulk. Delays are thus created between the instant a command to inject is received and the time that fuel is actually being injected into the engine intake duct. This basic limitation becomes more serious the higher the engine RPM's and calls for special injector designs even for regular fuel injection systems. This limitation becomes more severe when closed loop control is considered for fuel injected engines such as described in said SAE publication No. SP-393 (pages 137 to 144) for example. Faster, more efficient and responsive injectors are therefore needed inorder to improve the performance and efficiency of engine operation. It is therefore an object of this invention to provide faster, more powerful and more responsive injectors than presently available. It is yet a further object of this invention to provide actuating means for fast and responsive actuators controlling engine parameters.
A special type of parameter control is involved in engine optimizing systems such as described in said SAE publication (pages 155 to 182)--the so called dithering control. Dithering is required to provide sufficiently high modulation speeds and also waveforms that are not necessarily pulsed as in the case of fuel injection but belong to a wider class of waveforms. An example of a dither control can be seen in FIG. 13 on page 166 of said SAE publication. As shown, the speed of control may be sufficient for the purpose intended but the fuel to air ratio dither waveshape is there limited in both waveform and intensity. This limitation appears more severe when it is realized that the pressure in the intake duct of an internal combustion engine is strongly modulated by the periodic movements of the pistons and valves. It can now be recognized that the fuel to air ratio of the mixture flowing into the engine cylinders is a complex function of time indeed. It is therefore obvious that the dithering speed cannot be increased without a corresponding increase in the presence of extraneous modulation superimposed on the intended dithering signal waveform. An added complication is the non-linearity involved in the above dither which makes the associated system control circuits and in particular the engine efficiency or speed detection and processing circuits more complex and costly. It is therefore another object of this invention to provide increased modulation capabilities with regard to waveform and intensity and make this modulation largely independent of extraneous effects.
The expanding application of computers in general and in engine control in particular has introduced a very powerful and economical means for fast and complex processing of signals. Actuators for engine control parameters, on the other hand, are at present too slow in response and limited in their ability to produce a wide class of signals that is within the capability of computers to handle. This has created a need for faster and more responsive actuators. This need is, of course, not caused by the mere availability of computer processing power but rather by the great benefits to be derived from faster and more responsive actuators. To see this it is sufficient to consider the increase in engine efficiency or fuel economy that would result from faster tracking and more complete cancellation of engine perturbations caused by environmental changes. Considering, further, system diagrams, such as those shown in FIGS. 12 and 13 of said SAE publication on pages 165 and 166 for example, it can be seen that several system components must be improved inorder to improve the overall performance of the control system. It is thus necessary to increase the speed and responsiveness of the DITHER as well as those of the CELSIG and the SERVO inorder to get the full benefit from the increased speed of processing by the LOGIC circuits afforded by the computer. In fact, logic circuits, as is well known, can always be considered part of a computer and the increase in speed and capabilities of the computer means also corresponding increases in the logic. The computer can, however, do more than just improve the performance of logic; it can be used to replace many slow acting and bulky components of the control system. Virtually all hardware functions except the SERVO and DITHER output actuators can be replaced by computer software. The CELSIG unit, for example, which senses the engine acceleration is, in most embodiments, an electromechanical device. This entire unit may be replaced by measuring the frequency of the alternator (above SAE reference) and by feeding the measured values as input to the computer. The acceleration can then be derived by numerical processing as directed by the computer program and at processing speeds and accuracies that are far greater than those achievable by electromechanical SELSIG's. It may be noted at this point that the capabilities and techniques of computer system control are well known and appreciated and, by themselves, not essential for the understanding of this invention. Their discussion is nevertheless helpful in pointing out the problems that the present invention intends to solve. Considering further the above example of a CELSIG, the employment of the engine alternator as a source of speed information entails several limitations one of which involves electrical noise produced by mechanical vibrations. Clearly, an operating engine environment is a ready and constant source of such vibrations. The effect of the alternator is then made even more complex by the flexible belt that is usually employed to drive the alternator. The result is that acceleration values derived from the alternator output have noise superimposed on them so that the accuracy or resolution of the CELSIG is limited and this reduces the effectiveness of the optimizing system. It is therefore another object of this invention to provide an apparatus and a method for decoupling the actuator (the DITHER for example) from the mechanical and electrical environment of the engine and render the actuator modulation essentially independent of extraneous effects. Among the benefits to be derived from the increase in speed of response of control systems is the fact that perturbations of ever faster variations can be tracked more closely resulting in more complete cancellation of their adverse effects. This can be demonstrated by the example of an engine control system equipped with responsive actuators according to this invention and controlled preferably by a computer. The combustible mixture flowing into the engine cylinders has a waveform or modulation which is a complex function of time with frequency components corresponding to the speed of the engine. The engine frequency of revolution, for example, is one of the components but many more, including those of higher frequencies, are present in the mixture waveform. When the response speed of the engine control system is increased towards the range of the above modulation frequencies, and beyond, the stage is reached where the performance of the control system would start to degrade. This degradation can be avoided if the speed of response of the engine efficiency or speed or torque sensing elements of the control system is also increased. Considering, more particularly, an engine with a plurality of cylinders it can be appreciated that the combustible mixture modulation is likely to be different for each of the individual cylinders. If the control system does not take these differences into account and processes just average efficiency variations a significant improvement in performance may thereby be lost. If, on the other hand, signals generated by the engine speed sensor (for example) are processed so that accelerations due to individual cylinder power strokes are derived optimization of individual cylinder operation can be achieved. The engine acceleration due to individual power strokes can, for example, be derived by measuring the length of time between adjacent strokes of different cylinders. This time is shorter the higher the mechanical energy derived from a particular stroke and for a given resistance or engine load torque. Successive measurements of said lengths of time for the same ("dithered") cylinder provide a means for assessing the relative efficiencies of said cylinder power strokes. It is therefore another object of this invention to provide a new method and apparatus for actuating or dithering of individual parameters affecting engine efficiency. The resulting optimization and equalization of efficiencies between individual cylinders would reduce engine vibrations.
Vibrations in mechanical systems such as an engine with a large number of linkages, gears, bearings and the like are a source of dissipative energy losses, i.e. reduced efficiency, as well as a source for extra wear and surfaces deterioration. The increase in the above efficiency as well as the reduction of deterioration and wear are therefore other objects of this invention.